hwc: Support for reading FB format from driver

- Instead of assuming the default format(RGBA_8888),
  read FB format from driver and pass the info to SF
- For now, this is limited to primary and HDMI only.
  WB FBformat is assumed to be in RGBA_8888
- If FB doesn't have alpha channel, disable mixed mode

Change-Id: Iefc0080819749b541483ea47357bb37ec150c544
diff --git a/libhwcomposer/hwc_utils.h b/libhwcomposer/hwc_utils.h
index f11eed5..0008551 100644
--- a/libhwcomposer/hwc_utils.h
+++ b/libhwcomposer/hwc_utils.h
@@ -90,6 +90,7 @@
     float xdpi;
     float ydpi;
     bool secure;
+    uint32_t fbformat;
     int fd;
     bool connected; //Applies only to pluggable disp.
     //Connected does not mean it ready to use.
@@ -300,6 +301,7 @@
 void sanitizeSourceCrop(hwc_rect_t& cropL, hwc_rect_t& cropR,
                         private_handle_t *hnd);
 bool isAlphaPresent(hwc_layer_1_t const* layer);
+bool isAlphaPresentinFB(hwc_context_t* ctx, int dpy);
 int hwc_vsync_control(hwc_context_t* ctx, int dpy, int enable);
 int getBlending(int blending);
 bool isGLESOnlyComp(hwc_context_t *ctx, const int& dpy);